1. Field of the Invention
The present invention is directed to a vehicle door assembly line, such as, for automobiles, for assembling corresponding left and right doors.
2. Description of the Prior Art
Prior art automobile manufacturing processes include left door and right door assembly lines where different parts, such as door moulding, window regulator, handle, and window glass, are installed in the proper order. In the prior art, the left door and right door are assembled on separate assembly lines. Thus two assembly lines are required. As a result, two conveyor systems are needed which double the space of a single conveyor system.
One prior art improvement is described in Japanese Laid-Open Publication No. 6-285729. In this prior art system, a carrier with left and right vertical frames is driven to travel along a rail. A horizontal support member pivotally movable about a vertical axis is mounted on each of the vertical frames so that the left and right doors can be set on the support members separately. The parts are installed in the doors as left door and right doors are conveyed. In this prior art conveyor system, assembly workers standing on both right and left sides of the manufacturing line and are able to install parts on both the left and right doors simultaneously. Further, it is possible to turn both the left and right doors in a desired direction.
However, in this prior art pallet conveyor system, it is necessary to swing the right and left doors in the horizontal plane in order to assemble parts on both the interior and exterior sides of the left and right doors. Once the parts are assembled, the right and left doors are rotated or swung around to check the quality of the installation. This swinging operation reduces the work efficiency. Furthermore, it is necessary to provide adequate space to rotate around the left and right doors, and this requires an increase in the area required for the conveyor system.